Alterations of the cell surface are implicated in the changes in cell properties which accompany myoblast differentiation. An understanding of the changes in the surface membrane of cloned primary chick myoblasts during the various stages of differentiation forms the broad basis of this proposal. The surface membrane composition of different myoblast-types, inccuding a nerve-dependent myoblast, i.e., requires interaction with nerve for differentiation, will be examined. Surface phospholipids, fatty acids, cholesterol proteins and glycoproteins will be analyzed. Moreover, studies of the arrangement of these components during myoblast differentiation will be carried out using reagents, e.g., galactose oxidase-tritiated sodium borohydride and trinitrobenzene sulfonic acid, which react with external, accessible components. These combined studies should define surface membrane alterations related to primary chick myoblast differentiation and explore the basis for these alterations.